Acrylic resin-based coating agent compositions are used as coating agents for a variety of substrates used for building exteriors. A drawback with coating agent compositions of this type, however, has been their poor hardness, water repellency, durability, and adhesiveness to substrate. Quite a few coating agent compositions have heretofore been proposed in order to address this drawback. The following, for example, have been proposed: curable compositions in which the base component is a hydrolyzable silyl group-containing acrylic copolymer (refer to Patent References 1 and 2); a composition comprising a hydrolyzable silyl group-containing acrylic polymer, a silanol-functional organopolysiloxane, and a condensation reaction catalyst (refer to Patent Reference 3); and a composition comprising a condensation reaction-promoting catalyst, silanol-functional organopolysiloxane, and an acrylic polymer that contains both the hydroxyl group and a hydrolyzable silyl group (refer to Patent Reference 4). However, all of these compositions provide coating films that suffer from an inadequate water repellency and/or an inadequate durability.
The following have also been proposed: curable resin compositions (refer to Patent References 6 and 7) and a room-temperature-curable coating composition (refer to Patent Reference 5) comprising a siloxane-containing acrylic copolymer obtained by the copolymerization of an alkyl methacrylate, low molecular weight siloxane-containing methacrylate, and a silane compound that contains a hydrolyzable functional group and a radically polymerizable unsaturated group. However, the coating film yielded by this room-temperature-curable coating composition exhibits an inadequate water repellency due to the inadequate number of siloxane units in the low molecular weight siloxane-containing methacrylate. In addition, because the low molecular weight siloxane-containing methacrylate contains the dialkylsiloxane unit, the cured coating is soft and lacks an acceptable durability. Another drawback is that the low molecular weight siloxane-containing methacrylate is produced by a hydrosilylation reaction using a platinum catalyst; as a consequence, the coating film is prone to discoloration due to the platinum catalyst remaining in the room-temperature-curable coating composition.
The present inventors therefore proposed, in Patent Reference 8, a coating agent composition comprising an acrylic copolymer obtained by the radical polymerization of an acryloxy group-containing silane compound, a vinyl polymerizable unsaturated bond-containing compound, and an acryloxy group-containing siloxysilane compound (refer to Patent Reference 8). While this coating agent composition does cure to form a highly water-repellent, highly durable high-hardness cured film on substrates, the water repellency of the resulting cured film surface, the transparency, the durability, and the adhesiveness to substrate are not yet entirely satisfactory when this coating agent composition is used to coat a soft, lightweight substrate such as plastic substrates and particularly the transparent plastics used as glass substitutes (this application requires a long-term staining resistance and weathering resistance).    [Patent Reference 1] JP 02-064110 A    [Patent Reference 2] JP 03-024148 A    [Patent Reference 3] JP 03-252414 A    [Patent Reference 4] JP 07-150105 A    [Patent Reference 5] JP 03-069950 B    [Patent Reference 6] JP 04-103668 A    [Patent Reference 7] JP 10-101765 A    [Patent Reference 8] WO 2005/000981